Device for cooling food

ABSTRACT

An apparatus for cooling food, in particular water-based beverages, includes a cold accumulator ( 6 ) that contains a phase transition material. A conduit ( 8 ) for a water-based liquid that is to be chilled is guided through the cold accumulator ( 6 ). Also provided is a device ( 2 ) for dissipating heat from the cold accumulator ( 6 ). In order to make such an apparatus less expensive, easier to produce, and more effective, the cold accumulator ( 6 ) is made from a composite material containing expanded graphite and a phase transition material that undergoes a solid-liquid phase transition at or above 273 K.

The invention relates to an apparatus for cooling foods, in particularwater-based drinks, which is described in the preamble of claim 1.

Such an apparatus is disclosed by DE 198 56 214. In one embodiment ofthe known apparatus, a cold accumulator is provided in the form of anice bank which is cooled via a coolant by the cold side of a Peltierplate module. The drink to be cooled is passed round or through the icebank. The thermal conductivity of the ice water and therefore the heattransfer properties of the ice bank can be improved by distributing agood conductor, such as, for example copper wool or copper pieces, inits volume. The cooling of foods and drinks by ice is current practice,but has critical disadvantages. A main disadvantage is the low thermalconductivity of ice. The addition of copper material is firstlyexpensive and secondly involves the risk that, for example, copperpieces, under the influence of gravity, and with partial melting of theice bank, collect in the lower region and are depleted in the upperregion. A further disadvantage of ice which, however, has hithertoalways been accepted, is the unfavorable phase change temperature of iceto water, with to date there always being the risk, which had to beavoided by complex control technology, that also water-based drinksfroze. Although in this publication the use of a eutectic salt or analuminum block is mentioned as cold accumulator, the special choice ofthe eutectic salt, in particular according to its solid-liquid phasechange temperature, is not described however.

For industrial applications as tubular or plate heat exchanger, EP 914399 B1 discloses a composite material in which pressed expanded graphiteis impregnated with a phase change material. The graphite acts as heatconductor which in addition is able to take up the most varied phasechange materials. As phase change material, use can be made of paraffin,but preferably likewise water/ice.

In industrial and commercial applications, generally use is made ofcompression or absorption refrigeration units, the relatively largedimensions of which and also high production costs, oppose use in thedomestic sector, however. For this reason, for the provision of cooleddrinking water in the lower price segment, in particular in the field ofsmall domestic units, Peltier elements suggest themselves, in which, byapplying an electric field to two different electric conductors, oneside heats up and the other cools down.

Periodic provision of cooled drinking water for application in thedomestic sector, owing to the low thermal efficiencies of Peltierelements, make effective storage of, for example during night phases, acritical criterion for the capacity of a continuous flow Peltiercooling.

The simplest form of such a cooling is disclosed, for example, in DE 29910 820, in which a closed water reservoir is cooled down to the desiredtemperature by Peltier elements and replenishing water replaces acorresponding fraction of the cooled water. Since for storage of cold inthis case only the specific heat capacity of the water in the reservoiris available, large volumes are required even for small capacities.

U.S. Pat. No. 5,544,489 discloses in this respect an improvement incapacity by utilization of the melting enthalpy of the water to becooled. For this, on the cold side of the Peltier element, ice isgenerated within a water reservoir, as a result of which the energydensity of the cold accumulator is markedly increased.

However, both said apparatuses are opposed by the expected highmicrobial loading due to stagnant water in a reservoir with respect toapproval under drinking water law.

EP 0 777 090 provides an aid in this respect with the essentialdifference from U.S. Pat. No. 5,544,489 that the drinking water to becooled is passed through the ice-cooled reservoir in a pipe coil anddirect contact is therefore avoided. A problem in this regard of thespatial dimensions of such an apparatus is that the space filled by iceis no longer available for the drinking water coil.

A fundamental problem of all known continuous-flow Peltier-basedchillers is the low efficiency of Peltier elements which ispredominantly determined by the temperature difference between the coldand warm sides. Whereas the warm side, by use of corresponding coolingbodies and aeration fans, is problem-free in principle and technicallysolved, the cold side is a problem which has not yet been solved todate. Owing to the low specific thermal conductivity of the coldaccumulator medium used [λ_(water) approximately 0.57 W/(mK), λ_(ice)approximately 2.2 W/(mK)], there is an increase in the temperaturedifference and thus an impairment of the efficiency.

The object of the present invention is to provide an apparatus forcooling foods, in particular water-based drinks, which is simple andinexpensive to produce and has a high cooling capacity.

The object is achieved by the features specified in claim 1.

By means of the design according to the invention, for the first time anapparatus for cooling foods, in particular water-based drinks, isprovided which represents a high-grade solution for small equipment, inparticular in the household or restaurant. By means of the coldaccumulator used according to the invention and made of expandedgraphite and a phase change material which passes through itssolid-liquid phase change at or above 273 K, that is the freezingtemperature of water, preferably a few ° C. (up to 10° C.) above thefreezing point of water, a very effective cold accumulator is providedwhich firstly, as a result of the graphite, has a high thermalconductivity, and thereby ensures relatively rapid shock-like cooling,and which secondly comprises a phase change material which, even withoutcomplicated control technology, does not involve the risk thatwater-based drinks freeze and form an ice block. In addition, firstlythe size of the cold accumulator required for good performance isdecreased, and secondly the space and costs of comprehensive control aresaved.

Both measures lead to optimum matching of the apparatus according to theinvention to the requirements in the chilling of foods, in particularwater-based drinks.

Advantageous developments may be found in the subclaims.

To remove the heat taken up by the cold accumulator, preferably aPeltier element is provided which further has the advantage that theliquid flowing through the line can be heated for disinfection byreversing the polarity of the voltage supply of the Peltier element.Peltier elements are very cheap. The comparatively low thermalefficiencies of a Peltier element are of less importance owing to thevery effective storage material having expanded graphite, in particularwhen there is the possibility of being able to “charge” the coldaccumulator in idle times of the apparatus, for example during thenight.

However, instead of a Peltier element, conventional refrigeratortechnology can also be used, for example the absorber or compressortechnique for “charging” the cold accumulator. Thus it is conceivable,for example, to integrate the cold accumulator into a conventionalrefrigerator and there, either for equipping the refrigerator for activeand effective shock cooling, for example to use it in the area of thefreezer compartment, or to use it for dispensing a drink, for examplewater, from a central water supply, in or on the refrigerator, in thecourse of a shock-like continuous-flow cooling.

In principle, however, the invention may also be used advantageouslywherever a high cooling capacity with periodic load or fluctuatingcooling power requirement must be provided inexpensively with smallspatial dimensions.

In order that the entire container is available for the drinkingwater-bearing pipe geometry, in the invention use is made of a materialas cold accumulator medium which passes through a phase change at, or afew ° C. above, the freezing point of water, for which in principle salthydrates, eutectic mixtures and also paraffins are suitable.

To increase the efficiency of the Peltier element, the cold accumulatormedium is admixed with expanded graphite, as a result of which thethermal conductivity can be increased by up to a factor of 150.

The invention is in addition suitable for construction of a coolingcontainer, wherein the cold accumulator can be integrated into aninsulated wall of the cooling container, or into the interior, whereinthe interior can also be completely filled by the cold accumulator. Bymeans of the apparatus according to the invention, for exampleinexpensively available commercially conventional refrigerators can berefitted in this manner.

The invention can, for example, also be used as a shock-cooling unit fordispensing drinking water into a cooling container. The invention isalso particularly suitable for dispensing units, wherein, in theinterior of a housing, a drink source, for example a beer keg, can bereceived and the cold accumulator is active both in the interior and inthe dispense line.

Examples of the invention will be described in more detail hereinafterwith reference to the drawings. In the drawings:

FIG. 1 shows a diagrammatic representation of a first example of anapparatus according to the invention,

FIG. 2 shows the plan view onto FIG. 1,

FIG. 3 shows a diagrammatic representation of a further example of anapparatus according to the invention,

FIG. 4 shows the depiction of the section A-A from FIG. 3 for a firstarrangement of the line,

FIG. 5 shows the sectional view A-A from FIG. 3 for a second arrangementof the line,

FIG. 6 shows a diagrammatic representation of an apparatus according tothe invention using refrigerator technology.

FIG. 1 shows a device according to the invention for chilling foodshaving a cylindrical container 1 which has an introduced line in theform of a pipe coil 8 through which passes a water-based liquid to becooled from an inlet 5 to an outlet 4. The liquid to be cooled can beeither the drink to be cooled, preferably water with or without gasadmixture (carbon dioxide and/or oxygen) which originates from a watersource, preferably the central local water supply. Or, however, theliquid can be a coolant, which is, however, preferably likewise waterand originates from the central water supply, but serves for coolingfoods or drinks at another point.

The container 1 is filled by a cold accumulator 6 which comprises acomposite material made of expanded graphite and also a material whichpasses through a phase change at or above 273 K, the phase changepreferably being a few ° C. (up to 10° C., preferably 3° to 5° C.) abovethe freezing point of water.

Suitable phase change materials are preferably salts and also paraffinsknown for their phase change properties. In the example shown, thegraphite is present as free-flowing granules and is impregnated with thephase change material. The heat taken up from the liquid in the pipecoil 8 is taken off from the cold accumulator 6 again by a suitableunit. The unit in the example shown is a Peltier element 2 which is inintimate contact with the cold accumulator 6 by its cold side. The hotside of the Peltier element 2 is provided with an apparatus 3 fortransporting away the heat. The apparatus 3 can be any suitableapparatus and is in particular a fan as is customarily used with Peltierelements. In addition, measures can be taken to reverse the polarity ofthe Peltier element 2 so that if appropriate the liquid flowing throughthe line 8 can be heated for disinfection.

To improve the thermal conductivity, the point of the container 1 atwhich the Peltier element 2 is mounted is made of a readily-conductingmaterial, in particular a metallic material.

Finally, a plurality of Peltier elements can be provided.

In FIGS. 3 to 5, further examples of the apparatus according to theinvention for cooling foods are shown which differ from the exampleaccording to FIGS. 1 and 2 only by the details described hereinafter.The apparatus according to FIG. 3 also comprises a container 1 which inthis example, however, is rectangular, but can equally be cylindrical,as in the first example. In the container 1, a cold accumulator 6 isaccommodated which this time consists of plate-type, expanded graphitewhich was impregnated with the same phase change material which hasalready been described with reference to FIG. 1. The cold accumulatorhas a layer structure, with plates of the graphite material alternatingwith a layer-type arrangement 7 of suitably shaped and laid lines which,however, again extend from the container 1 by the water outlet 4 and thewater inlet 5. The layer-type arrangement 7 can contain, for example, ameander-like line geometry 9 of FIG. 4 or a spiral-type line geometry 10of FIG. 5. Each line layer 7 is connected by inlet and outlet in amanner which is not shown to the adjacent line layers, with the firstand last line layers being connected to the water outlet 4 and the waterinlet 5, respectively.

The line layers can either be laid as pipes, or in the shape of profiledplates, wherein preferably two plates are provided in a mirror imagefashion with corresponding embossings of the size of the half crosssection of the line, and the plates are subsequently laid one upon theother and are fastened to one another, so that the embossings supplementeach other to give continuous channels which are closed on the peripheryside. Not only the pipes but also the profile plates consist of readilyheat-conducting material, for example metal. The lines 8, 9 or 10preferably have a diameter between 3 and 11 mm, in particular 4-10 mm,since, with this diameter, in combination with a water pressure as issupplied on average by a water pipe grid (1.5-4.5 bar) which, ifappropriate, can be set by a pump or a pressure-reducing valve to aconstant insignificantly varying pressure (±0.5 bar), a strong flowcounteracting microbial infestation forms.

The layer-like arrangement according to FIGS. 3 to 5 is preferablyproduced by compressing the line layers having the graphite plates,which leads to a particularly intimate, heat-transferring contactbetween the layers.

In this example also, the system for “charging” the cold accumulator 6preferably contains the Peltier element 2 already described, wherein thePeltier element 2 is arranged in such a manner that the surface normalto the graphite plates is oriented in parallel to the surface of thePeltier element 2.

The examples corresponding to FIGS. 1 to 5 are preferably constructed inthe form of a cold battery, that is to say a handleable unit. In thisform, the apparatus according to the invention can be installed anywherewhere it is required, if appropriate even retrospectively. It is onlynecessary that measures are taken to connect the water inlet and outlet4, 5 to a water source, for example the local drinking water supply.However, if appropriate, it is also possible to construct the apparatusaccording to the invention as a cold battery without the Peltier elementand to use another technology for “charging” the cold accumulator.

This can be, for example, the cooling unit of a conventionalrefrigerator, for example an absorber or compressor refrigerator. Thiscase is illustrated in FIG. 6. FIG. 6 shows a conventional refrigerator11 which is provided with its own cooling unit 12. In the refrigerator11 a cold accumulator 6 of the invention is installed which isconstructed as a cold battery. The cold accumulator 6 can, as shown inFIG. 6, be accommodated anywhere in the interior 13 of the refrigerator11, if appropriate also retrospectively. In the example shown, it isaccommodated in the rear region opposite a door 14. The cold accumulator6, however, can also be accommodated anywhere in a wall 15 (includingbase and upper cover or door 14) or in an intermediate base or the like.

The cold accumulator 6 is provided with the line 8 through which awater-based liquid is passed. The water inlet 5 is connected to adrinking water grid which is preferably detachable via a valve 5 a, forexample a conventional water tap. The water outlet 4 can be passed to adispense point which is not shown.

The function of the Peltier element, here, however, is met by thecooling unit 12 of the refrigerator 11. The cold accumulator 6 can, asshown, be provided only in one part of the interior 13, but can alsofill the entire interior 13.

The latter version leads to an apparatus for cooling drinks which can bemanufactured particularly inexpensively, the line being passed throughthe entire interior filled with cold accumulator 6.

1-12. (canceled)
 13. An apparatus for cooling foods, comprising: a coldaccumulator containing expanded graphite and a phase change materialconfigured to pass through a solid-liquid phase change at or above 273K; a line for conducting a water-based liquid to be cooled through saidcold accumulator; and a device for removing heat from said coldaccumulator.
 14. The apparatus according to claim 13, configured to coolwater-based beverages.
 15. The apparatus according to claim 13, whereinsaid cold accumulator contains a loose bed of graphite granulesimpregnated with said phase change material.
 16. The apparatus accordingto claim 13, wherein said phase change material has a phase changetemperature not above 10° C.
 17. The apparatus according to claim 13,wherein said phase change material has phase change temperature above 0°C. and not above 10° C.
 18. The apparatus according to claim 13, whereinsaid device for removing heat contains a Peltier element.
 19. Theapparatus according to claim 18, wherein said Peltier element isconnected to a reversible voltage supply and the liquid flowing throughsaid line is heatable for disinfection by reversing a polarity of thevoltage supply of said Peltier element.
 20. The apparatus according toclaim 13, wherein said device for removing heat includes an absorberand/or evaporator refrigeration unit.
 21. The apparatus according toclaim 13, configured as a cold battery having at least one coldaccumulator as a portable unit.
 22. The apparatus according to claim 21,wherein said portable unit includes said device for removing heat. 23.The apparatus according to claim 13, wherein said line is connected to adrink source and leads to a dispensing system.
 24. The apparatusaccording to claim 13, wherein said line is connectible to a centralwater supply.
 25. The apparatus according to claim 13 configured as acooling container, which comprises a housing with an insulated wall andsaid cold accumulator and said line integrated in said wall and/ordisposed in an interior of said housing.